M45PE40-VMP6 datasheet(8/35 Pages) STMICROELECTRONICS

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M45PE40

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mode until another specific instruction (the Re-

lease from Deep Power-down and Read Electron-

ic Signature (RES) instruction) is executed.

All other instructions are ignored while the device

is in the Deep Power-down mode. This can be

used as an extra software protection mechanism,

when the device is not in active use, to protect the

device from inadvertent Write, Program or Erase

instructions.

Status Register

The Status Register contains two status bits that

can be read by the Read Status Register (RDSR)

instruction.

WIP bit. The Write In Progress (WIP) bit indicates

whether the memory is busy with a Write, Program

or Erase cycle.

WEL bit. The Write Enable Latch (WEL) bit indi-

cates the status of the internal Write Enable Latch.

Table 2. Status Register Format

Note: WEL and WIP are volatile read-only bits (WEL is set and re-

set by specific instructions; WIP is automatically set and re-

set by the internal logic of the device).

Protection Modes

The environments where non-volatile memory de-

vices are used can be very noisy. No SPI device

can operate correctly in the presence of excessive

noise. To help combat this, the M45PE40 features

the following data protection mechanisms:

■

Power On Reset and an internal timer (tPUW)

can provide protection against inadvertant

changes while the power supply is outside the

operating specification.

■

Program, Erase and Write instructions are

checked that they consist of a number of clock

pulses that is a multiple of eight, before they

are accepted for execution.

■

All instructions that modify data must be

preceded by a Write Enable (WREN)

instruction to set the Write Enable Latch

(WEL) bit. This bit is returned to its reset state

by the following events:

–

Power-up

–

Reset (RESET) driven Low

–

Write Disable (WRDI) instruction

completion

–

Page Write (PW) instruction completion

–

Page Program (PP) instruction completion

–

Page Erase (PE) instruction completion

–

Sector Erase (SE) instruction completion

■

The Hardware Protected mode is entered

when Write Protect (W) is driven Low, causing

the first 256 pages of memory to become

read-only. When Write Protect (W) is driven

High, the first 256 pages of memory behave

like the other pages of memory

■

The Reset (Reset) signal can be driven Low to

protect the contents of the memory during any

critical time, not just during Power-up and

Power-down.

■

In addition to the low power consumption

feature, the Deep Power-down mode offers

extra software protection from inadvertant

Write, Program and Erase instructions while

the device is not in active use.

WEL

WIP

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